Signal Detection Device, Signal Detection Circuit, Signal Detection Method, And Program

ABSTRACT

A signal detection device rapidly and accurately detects a desired signal from a reception signal. A correlation unit  231  outputs a correlation value string obtained by cross-correlating an input symbol string and a reference symbol string, a first position detection unit  232  detects a position of a correlation value viewed as a maximum or a local maximum on the correlation value string, a compensation unit  233  performs compensation by suppressing correlation error values from correlation value at positions other than the detected position, a second position detection unit  234  detects a position of a correlation value viewed as the maximum on the compensated correlation value string, and a sync-detected signal generation unit  235  outputs a sync-detected signal based on the position detected by the second position detection unit  234.

TECHNICAL FIELD

The present invention relates to technology for cross-correlating areceived input signal and a known reference signal to detect a desiredsignal, and in particular to technology for rapidly and accuratelydetecting a desired signal in a poor channel environment.

BACKGROUND ART

Conventionally, in terrestrial wireless communication and wirelessbroadcasting for mobile phones, televisions and the like, signalstransmitted from a base station etc. are distorted due to the effects ofwhite noise and multipath, thereby making it impossible for a receptiondevice receiving such signals to properly detect a synchronizing signalincluded therein.

The following patent document 1 discloses a signal detection device as aconventional signal detection device for detecting a synchronizingsignal.

FIG. 21 shows a functional structure of the signal detection devicedisclosed in patent document 1.

A signal detection device 1000 includes a correlating unit 1001, amaximum value position detector 1002 and a reliability measurer 1003.

The correlating unit 1001 cross-correlates an input signal (i.e., areceived signal) and a known synchronizing signal on the receiving side,the maximum value position detector 1002 detects a peak position in aresulting string of correlation values, and the reliability measurer1003 checks whether the position detected by the maximum value detector1002 is the proper position of the synchronizing signal, therebymeasuring the reliability of the detected position.

Patent Document 1: U.S. Pat. No. 6,504,578

DISCLOSURE OF THE INVENTION Problems Solved by the Invention

However, the signal detection device of patent document 1 has a problemwith speed since it is necessary to detect a position a number of timesto achieve reliability, and even when the above reliability measuring isperformed, there still remains the possibility of detecting an erroneousposition as the synchronizing signal position.

This is because the maximum value may appear at an erroneous positiondue to the signal, which was distorted by a poor channel environment,including components that have been affected by white noise andmultipath.

The present invention has been achieved to solve the above problem, andaims to provide a signal detection device, signal detection circuit,signal detection method, and computer program that can rapidly andaccurately detect a desired signal from a reception signal that has beendistorted in a poor channel environment.

Means to Solve the Problems

The above object of the present invention is achieved by a signaldetection device, including: a correlation unit operable to output acorrelation value string based on a result of cross-correlating areference signal value string included in an input signal value stringand signal value strings that are obtained by shifting a certain signalvalue string one by one in order of the input signal value string andthat correspond in length to the reference signal value string; and acompensation unit operable to perform compensation by obtaining acorrelation error of at least one of the output correlation values andsuppressing the correlation error from the at least one correlationvalue.

Also, a signal detection circuit of the present invention is a signaldetection circuit, including: a correlation circuit operable to output acorrelation value string based on a result of cross-correlating areference signal value string included in an input signal value stringand signal value strings that are obtained by shifting a certain signalvalue string one by one in order of the input signal value string andthat correspond in length to the reference signal value string; and acompensation circuit operable to perform compensation by obtaining acorrelation error of at least one of the output correlation values andsuppressing the correlation error from the at least one correlationvalue.

Also, a signal detection method of the present invention is a signaldetection method for performing compensation by obtaining a correlationerror of at least one correlation value on a correlation value stringthat is based on a result of cross-correlating a reference signal valuestring included in a signal value string and signal value strings thatare obtained by shifting a certain signal value string one by one inorder of the signal value string and that correspond in length to thereference signal value string, and suppressing the correlation errorfrom the at least one correlation value.

Also, a program of the present invention is a computer program forcausing a signal detection device or a signal detection circuit toexecute signal detection processing, wherein the signal detectionprocessing includes a compensation step of performing compensation byobtaining a correlation error of at least one correlation value on acorrelation value string that is based on a result of cross-correlatinga reference signal value string included in a signal value string andsignal value strings that are obtained by shifting a certain signalvalue string one by one in order of the signal value string and thatcorrespond in length to the reference signal value string, andsuppressing the correlation error from the at least one correlationvalue.

EFFECTS OF THE INVENTION

The signal detection device having the above structure performscompensation by suppressing correlation errors from correlation valuesbased on a result of cross-correlation an input signal value string anda reference signal value string.

This structure makes it possible to suppress a correlation error from acorrelation value that has been detected as the maximum and includescomponents affected by multipath, and detect the position of an accuratemaximum from the compensated correlation value string. In other words,this structure enables the accurate detection of a desired signal.

It is also possible to rapidly perform detection since it is notnecessary to repeatedly detect a sync position until reliability isobtained, as in the signal detection device disclosed in the abovepatent document.

Also, the signal detection device may further include: a first positiondetection unit operable to detect a first position in the correlationvalue string output by the correlation unit, the first position beingbased on a position of a correlation value viewed as a maximum or alocal maximum, wherein the compensation unit performs the compensationby obtaining the correlation error of the correlation value at least oneposition other than the first position detected by the first positiondetection unit, and suppressing the correlation error from the at leastone correlation value, may further include: a second position detectionunit operable to detect a second position in the correlation valuestring compensated by the compensation unit, the second position beingbased on a position of a correlation value viewed as a maximum on thecompensated correlation value string, and the compensation unit mayperform the compensation by associating the first position detected bythe first position detection unit and a position of a maximum on acorrelation error value string that is based on a result ofcross-correlating the reference signal value string and signal valuestrings which are obtained by shifting a certain signal value string oneby one in order of a known signal value string including the referencesignal value string and which correspond in length to the referencesignal value string, and suppressing, based on a correlation error valueat a position in the correlation error value string corresponding to asecond position other than the first position, the correlation errorfrom a correlation value at the second position.

Also, a second reference signal value string specifying a polarity maybe included in the input signal value string, the signal detectiondevice may further include: a second correlation unit operable to outputa second correlation value string based on a result of cross-correlatingthe second reference signal value string and signal value strings thatare obtained by shifting a certain signal value string one by one inorder of the input signal value string and that correspond in length tothe second reference signal value string; and a polarity detection unitoperable to output a polarity that is specified based on a position of acorrelation value viewed as a maximum or a local maximum on the secondcorrelation value string output by the second correlation unit, and thecompensation unit may perform the compensation based on the polarityspecified by the polarity detection unit and the correlation error.

According to this structure, regarding the compensation unit, an inputsignal that includes a second reference signal value string indicatingpolarity can be applied in a case of detecting a synchronization signal.

Also, a third reference signal value string specifying a signal mode ofan input signal may be included in the input signal value string, thesignal detection device may further include: a mode detection unitoperable to detect the third reference signal value string based on theinput signal value string, and the compensation unit may perform thecompensation based on a signal mode detected by the mode detection unitand the correlation error.

According to this structure, the compensation unit can use an inputsignal that includes a third reference signal value string indicating asignal mode, for synchronization signal detection.

Also, the first position detection unit may detect a maximum positionthat is a position corresponding to a correlation value viewed as themaximum on the correlation value string, and a local maximum positionthat is a position corresponding to a correlation value viewed as thelocal maximum on the correlation value string, and the compensation unitmay perform the compensation by one of associating the local maximumposition and a position of a maximum on a correlation error value stringthat is based on a result of cross-correlating the reference signalvalue string and signal value strings which are obtained by shifting acertain signal value string one by one in order of a known signal valuestring including the reference signal value string and which correspondin length to the reference signal value string, obtaining a correlationerror value on the correlation error value string at a positioncorresponding to the maximum position, and suppressing, based on thecorrelation error value, a correlation error from the correlation valueat the maximum position, and associating the maximum position and aposition of a maximum on the correlation error value string, obtaining acorrelation error value on the correlation error value string at aposition corresponding to the local maximum position, and suppressing,based on the correlation error value, a correlation error from thecorrelation value at the local maximum position.

This structure enables the precise suppression of correlation errors incompensation processing.

Also, the first position detection unit may detect a maximum positionthat is a position in the correlation value string which corresponds toa correlation value viewed as the maximum, and a local maximum positionthat is a position in the correlation value string which corresponds toa correlation value viewed as the local maximum, and the compensationunit may perform the compensation by associating the maximum positionand a position of a maximum on a correlation error value string that isbased on a result of cross-correlating the reference signal value stringand signal value strings which are obtained by shifting a certain signalvalue string one by one in order of a known signal value stringincluding the reference signal value string and which correspond inlength to the reference signal value string, obtaining a firstcorrelation error value on the correlation error value string at aposition corresponding to the local maximum position, associating thelocal maximum position and the position of the maximum on thecorrelation error value string, obtaining a second correlation errorvalue on the correlation error value string at a position correspondingto the maximum position, and one of suppressing, based on a firstcomposite correlation error value obtained by subtracting the secondcorrelation error value from the first correlation error value, acorrelation error from the correlation value at the local maximumposition, and suppressing, based on a second composite correlation errorvalue obtained by subtracting the first correlation error value from thesecond correlation error value, a correlation error from the correlationvalue at the maximum position or the local maximum position.

This structure reduces the number of operations performed incompensation processing.

Also, the compensation unit may output a value that is based on acompensated correlation value string to at least one of an equalizationunit, a spectrum conversion unit, and a channel response measuring unit.

According to this structure, it is possible to use the compensatedcorrelation value string for generation of a filter coefficient used inequalization, or the measurement of spectrum or channel response.

Also, if a currently detected position differs from a previouslydetected position, the second position detection unit may output anamount of change therebetween.

According to this structure, it is possible to convey a shift in thebasis position separately from channel response when, for example, usingchannel response with respect to something other than signal detection,such as equalization.

Also, the signal detection circuit may further include: a first positiondetection circuit operable to detect a first position in the correlationvalue string output by the correlation circuit, the first position beingbased on a position of a correlation value viewed as a maximum or alocal maximum; and a second position detection circuit operable todetect a second position in the correlation value string compensated bythe compensation circuit, the second position being based on a positionof a correlation value viewed as a maximum on the compensatedcorrelation value string, wherein the mode detection circuit mayinclude: a third correlation circuit operable to specify a positionsection of a mode signal value string in the input signal with use ofoutput from the first position detection circuit or the second positiondetection circuit, and cross-correlate a signal value string in theposition section and a third reference signal value string that is atleast a part of one of a plurality of the mode signal value strings eachof which is for identifying a different one of the signal modes; acumulative addition circuit operable to cumulatively add correlationvalues calculated by the third correlation circuit to the plurality ofmode signal value strings N times, N being a natural number; and a modespecification circuit operable to specify, from among the plurality ofmode signal value strings, a mode signal value string having a highestvalue cumulatively added by the cumulative addition circuit, as a signalmode of the input signal string.

This structure enables the accurate detection of a signal in a severemultipath environment, and more accurate mode detection when there isnoise and severe multipath by taking a correlation using a signal beforehard-decision.

Also, the signal detection circuit may further include: a first positiondetection circuit operable to detect a first position in the correlationvalue string output by the correlation circuit, the first position beingbased on a position of a correlation value viewed as a maximum or alocal maximum; and a second position detection circuit operable todetect a second position in the correlation value string compensated bythe compensation circuit, the second position being based on a positionof a correlation value viewed as a maximum on the compensatedcorrelation value string, wherein the mode detection circuit mayinclude: a third correlation circuit operable to output correlationvalues with respect to a certain mode signal value string by specifyinga position section of a mode signal value string in the input signalwith use of output from the first position detection circuit or thesecond position detection circuit, and cross-correlating a signal valuestring in the position section and a third reference signal value stringthat is at least a part of one of a plurality of the mode signal valuestrings each of which is for identifying a different one of the signalmodes, and output values obtained by inverting a sign of the correlationvalues as correlation values with respect to another mode signal valuestring; a cumulative addition circuit operable to cumulatively addcorrelation values calculated by the third correlation circuit to theplurality of mode signal value strings N times, N being a naturalnumber; and a mode specification circuit operable to specify, from amongthe plurality of mode signal value strings, a mode signal value stringhaving a highest value cumulatively added by the cumulative additioncircuit, as a signal mode of the input signal string.

When detection is limited to two candidate modes, this structure enablesmode detection by performing a single correlation operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary functional structure of a broadcast receptiondevice;

FIG. 2 shows a functional structure of a sync detection unit accordingto embodiment 1;

FIG. 3 shows an exemplary structure of a correlation unit;

FIG. 4 shows a data structure of a VSB data frame in the ATSC system;

FIG. 5 is a graph showing an exemplary correlation value string obtainedas a result of cross-correlating an input symbol string and a referencesymbol string;

FIG. 6 is a graph showing a correlation value string obtained bycross-correlating a known first field sync segment and a referencesignal value string which is a part of a PN511 symbol string;

FIG. 7 is an exemplary graph showing a correlation error value stringobtained by cross-correlating the known first field sync segment and thereference signal value string which is a part of the PN511 symbolstring, where the correlation error value string has been normalized andt=0 is a position of a maximum;

FIG. 8 is a table showing an exemplary correlation error value string;

FIG. 9A is a table showing the correlation value string of FIG. 5normalized considering a correlation value at T=9 to be the basis andincluding correlation values at positions before and after T=9, and FIG.9B is a table showing the correlation value string of FIG. 9A aftercompensation processing has been performed;

FIG. 10A is a table showing the correlation value string of FIG. 5normalized considering a correlation value at T=11 to be the basis andincluding correlation values at positions before and after T=11, andFIG. 10B is a table showing the correlation value string of FIG. 10Aafter compensation processing has been performed;

FIG. 11 is a flowchart for describing operations of compensationprocessing 2;

FIG. 12A is a table showing a correlation value string resulting fromthe correlation value string in FIG. 9A being compensated bycompensation processing 2, and FIG. 12B is a table showing a correlationvalue string resulting from the correlation value string in FIG. 10Abeing compensated by compensation processing 2;

FIG. 13 is a flowchart for describing operations of compensationprocessing 3;

FIG. 14 is a table showing the correlation value string shown in FIG. 9Aafter compensation processing has been performed;

FIG. 15 shows a functional structure of a sync detection unit accordingto variation 1;

FIG. 16 shows a functional structure of a sync detection unit accordingto variation 2;

FIG. 17 shows a functional structure of a mode detection unit accordingto embodiment 2;

FIG. 18 is a table showing 24-bit data of VSB modes in the ATSC system;

FIG. 19 shows a functional structure of a mode detection unit accordingto variation 3;

FIG. 20 shows a functional structure of a mode detection unit accordingto variation 4;

FIG. 21 shows an exemplary functional structure of a conventional signaldetection device; and

FIG. 22 is a graph showing a correlation value string obtained byautocorrelating a PN symbol string.

DESCRIPTION OF THE CHARACTERS

-   -   1 broadcast reception device    -   2 front-end unit    -   3 back-end unit    -   21 tuner    -   22 demodulation unit    -   23 sync detection unit    -   24 equalization unit    -   25 error correction unit    -   231 correlation unit    -   232 first position detection unit    -   233, 233A, 233B compensation unit    -   234 second position detection unit    -   235 synchronization-detected signal generation unit    -   236 second correlation unit    -   237 polarity detection unit    -   238 field number signal generation unit    -   239, 239A, 239B, 239C mode detection unit    -   240 VSB mode signal generation unit    -   501 third correlation unit    -   502, 504, 603 mode specification unit    -   503, 602 cumulative addition unit    -   601 distance calculation unit

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are described below with referenceto the drawings.

Embodiment 1

Functional Structure of a Broadcast Reception Device

FIG. 1 shows a functional structure of a broadcast reception device thatuses a signal detection device of the present invention as a syncdetection unit.

A broadcast reception device 1 is a reception device compatible with thesingle carrier 8 level VSB (Vestigial Sideband) modulation system calledthe ATSC (Advanced Television Systems Committee) system, which is theterrestrial digital broadcasting method used in the United States. Thebroadcast reception device 1 is functionally divided into a front-endunit 2 and a back-end unit 3. As shown in FIG. 1, the front-end unit 2and the back-end unit 3 are realized by an integrated circuit.

The front-end unit 2 includes a tuner 21, a demodulation unit 22, a syncdetection unit 23, an equalization unit 24 and an error correction unit25.

The tuner 21 tunes to a received VSB-modulated broadcast signal.

The demodulation unit 22 demodulates the tuned VSB-modulated broadcastsignal and outputs a symbol string of a VSB signal. A data structure ofa VSB signal is described later.

The sync detection unit 23 detects a segment synchronization signal anda field synchronization signal from a symbol string.

The equalization unit 24 suppresses distorted components in a symbolstring distorted by multipath.

The error correction unit 25 corrects code error generated on a channel,and outputs a transport stream.

The back-end unit 3 receives the transport stream output from thefront-end unit 2, converts the received transport stream to videosignals, audio signals and the like, and outputs the video and audiosignals and the like.

VSB Data Frame Structure

Next is a description of VSB data frames in the ATSC system.

FIG. 4 shows a data structure of a VSB data frame in the ATSC system.

A VSB data frame is constituted from two fields, a first field and asecond field.

A field is composed of 313 segments, and the first segment is a fieldsync segment. The first and second fields can be differentiated due tothe fact that the polarity of the second of three PN63 symbol stringsincluded in the field sync segment is inverted.

Segments other than the first segment are composed of a segment syncsymbol string (4 symbols) and a data symbol string (828 symbols). In8-VSB mode, a symbol is made up of 3 bits.

The field sync segment is composed of a segment sync (4 symbols), atraining signal (724 symbols), and a reserved area etc. (104 symbols).

The training signal is a pseudo noise signal taking pseudo random valuesin a signal bandwidth. The training signal is composed of a PN511 symbolstring (511 symbols), three PN63 symbol strings (63 symbols each, atotal of 189 symbols), and a VSB mode symbol string (24 symbols) foridentifying one of the five VSB modes, 2-VSB, 4-VSB, 8-VSB, 16-VSB andTC 8-VSB.

In 8-VSB mode, data symbols constituting a data segment are encodedinformation such as video, audio, data, etc., and are represented as,for example, the eight value levels, +7, +5, +3, +1, −1, −3, −5, and −7.

In 8-VSB mode, symbols in the segment sync symbol string and the fieldsync symbol string are represented as, for example, the two value levels+5 and −5, with the exception of a portion of the reserved symbolstring.

In the present invention, the above-mentioned segment sync and trainingsignal are targets of detection by the sync detection unit 23.

Outline of Sync Detection Processing

One example of a method of detecting the above synchronization signal ina conventional signal detection device involves detection using acorrelation operation. This method is effective in cases where thedetected signal has a high autocorrelativity and there is a steep peakin the result of the correlation operation. This is because it ispossible to detect the peak position without error even if some noise orthe like is included in the detected signal, since there is a largedifference between the peak and other values, thereby making it possibleto detect a desired signal from the peak position.

Given that autocorrelation is a correlation operation performed betweena signal and itself, and a correlation operation obtains an innerproduct of signals that have been shifted and an un-shifted signal, itis apparent from looking at an actual correlation value string thatthere is only a peak in a case of signal with a high autocorrelativity,i.e. having a small correlativity value with its own shifted signal, ata correlation value between un-shifted signals.

FIG. 22 is a graph showing a correlation value string obtained byautocorrelating a PN symbol string.

As shown in FIG. 22, the correlation value string obtained byautocorrelating the PN symbol string has a characteristic in which allcorrelation values other than the peak appearing when theautocorrelativity is high are a known constant value. In other words,the correlation value string obtained by autocorrelating the PN symbolstring is composed of two types of values, namely the peak value and allother values.

In contrast, a transmitted transmission signal includes not only the PNsymbol string, but also arbitrary data symbol strings before and after,and when the PN symbol string is detected as a reference symbol string,the result of a correlation between the transmission signal and thereference symbol string is a value string that is clearly different fromthe above-mentioned correlation value string obtained by autocorrelatingthe PN symbol string, and as in FIG. 6 which is mentioned later,correlation values other than the peak value become arbitrary valuesthat differ according to their position (i.e., correlation noise).

Also, transmission signals are largely affected by mainly noise andmultipath on terrestrial broadcasting channels and the like. When atransmission signal picks up noise etc. on the channel and is receivedby a reception device as an input signal, effects of the noise appear inthe correlation value string of the input signal. However, effects ofthe noise component in the input signal are reduced due to beingsuperimposed between input signal values by a correlation operation, andperforming detection using peak detection results in two or more signalsections enables further reduction of the effects of the noisecomponents.

Input signals that are affected by multipath and received by a receptiondevice include not only the directly transmitted signal, but alsosignals that have reflected off of various objects such as buildings.Such signals from reflex pathways have different amplitudes and arrivaltimes from the direct pathway signal. In other words, the input signalis a composited signal including the direct pathway signal and a numberof reflex pathway signals.

The effects of such multipath can be reduced by an equalization filteror the like, and since it is advantageous in equalization to generate afilter coefficient by a training method using a synchronization signalincluded in the input signal, it is necessary to detect thesynchronization signal before performing equalization, therefore makingit necessary in this case to detect the synchronization signal from thesignal affected by multipath.

Consequently, when a correlation operation is performed to detect asynchronization signal in the input signal, not only does the resultingcorrelation value string include effects of noise and multipath on thechannel, but effects of the above-mentioned correlation noise also makedetection of the synchronization signal difficult, and may lead to afalse detection of the synchronization timing.

For example, in the case of multipath, if the amplitude of a reflexpathway signal approaches the amplitude of the direct pathway signal,similar signals having different arrival times are receivedcollectively, and a correlation result of the received signals willtherefore have two or more peaks with similar amplitudes, thereby makingit necessary to discern which peak to detect as the synchronizationposition. Here, a signal whose path has a stronger reception power isthought to have a higher peak since peak amplitude indicatescorrelativity, and therefore detecting the synchronization signal in thedirect pathway signal that has the highest reception power etc. isperformed by detecting the highest peak position as the synchronizationposition.

However, as the peak values change due to noise etc., the magnituderelation between peaks when there is no noise is lost, and there is thepossibility, when there is noise, of falsely detecting a peak other thanwhat would be the maximum peak if there were no noise. This noiseincludes not only noise on the channel, but also correlation noise fromthe correlation operation used in the detection, and there is an evenfurther increased possibility of making a false detection since bothtypes of noise cannot be separated. Even if the effects of this noiseare mitigated by performing synchronization detection using theabove-mentioned result of detecting two or more peaks or the like,effects of this noise will still remain.

The present invention therefore proposes a method of further reducingeffects of noise and multipath by suppressing correlation errorscorresponding to correlation noise in noise that affects detection ofthe synchronization signal by a correlation operation.

First, since correlation noise is generated due to arbitrary data symbolstrings before and/or after the reference symbol string, a known symbolstring is provided in the transmission signal between the referencesignal string and data symbol strings before and/or after the referencesignal string. When a reception device receives such a transmissionsignal as an input signal, and the input signal and the reference symbolstring are cross-correlated, a known correlation value string, that is,a correlation error value string, will appear before and/or aftercorrelation peaks in the resulting correlation value string. Thecorrelation values of this correlation error value string can bearbitrary values, but differ from unpredictable correlation noise. Notethat if the known symbol string is not provided, a part of the originalreference symbol string can be used as the known symbol string byshortening the reference symbol string. However, the magnitude of thepeaks will be reduced and correlation values other than the peaks willbe increased when the reference symbol string is shortened, but thiseffect may be ignored.

By suppressing (e.g., removing) this correlation error value string fromthe correlation value string obtained by correlating the input signaland the reference signal, portions of the correlation value string inthe vicinity of the peaks appear to include only two type of values asin a correlation value string obtained by autocorrelation, and even ifchannel noise is added to the input signal, the suppression of thecorrelation error value string makes it much more difficult to make afalse detection, compared with when correlation noise is included. Inother words, it is possible to increase performance for detecting thesynchronization signal. Since correlation errors may change depending onthe position of the correlation value on the correlation value string,correlation errors can be obtained according to positions on thecorrelation value string, and a peak or the like may be used as areference for such positions. Detecting a peak after such compensationmakes it possible to obtain the position of the synchronization signalwithout correlation errors.

The following considers a case of losing the above-mentioned magnituderelation between peaks due to correlation error in the correlation valuestring of the input signal as a result of the effects of multipath, andfalsely detecting a synchronization signal. Since the input signal is acomposite signal including signals from the direct pathway and reflexpathways, and the correlation operation is a linear operation, thecorrelation value string of the input signal becomes a composite valuestring including the correlation value strings of the direct pathwaysignal and the reflex pathway signals. The direct pathway signals andthe reflex pathways signals differ with respect to amplitude and arrivaltime, and since these original signals without these differences are thesame transmission signals, substituting the amplitude and time of thecorrelation value string for the direct pathway signal with theamplitude and time of that for a reflex pathway signal results in thecorrelation value string for the reflex pathway signal. Therefore in thecorrelation value string of the input signal, a peak in the correlationvalue string for the direct pathway signal includes a correlation errorat a corresponding time on the correlation value string for the reflexpathway signal, or on the other hand, a peak of the correlation valuestring for the reflex pathway signal includes a correlation error at thecorresponding time on the correlation value string for the directpathway signal.

For this reason, as the amplitudes of the reflex pathway signalsapproach the amplitude of the direct pathway signal as mentioned above,correlation errors cause the peaks of the reflex pathway signals havinga smaller reception power to be bigger than the peak of the directpathway signal having a greater reception power, whereby the magnituderelation is lost, and the possibility of a false detection increases.

Therefore, several peaks are obtained from the correlation value stringof the input signal, a correlation error with respect to each of thepeaks is obtained by utilizing the fact that each of the peaks is a partof a correlation value string having a correlation error, and each ofthe peaks is better compensated by suppressing the correlation errorsresulting from the addition of other peaks. Given that it is difficultto obtain a right peak without a correlation error before compensationsince each of the peaks includes a correlation error corresponding toanother peak, it becomes difficult to properly obtain the correlationerror of the peak; assuming that the correlation error with respect tothe right peak is random such as noise at the position corresponding tothe peak, the positions of other peaks with respect to a certain peakbecome arbitrary, and when a number of correlation errors with respectto other peaks are composited on the certain peak, the correlationerrors are composited at random positions, whereby not only the effectsof synchronous addition noise decrease, but also correlation errorsversus the peaks are small as shown in, for example, FIG. 6, wherebytheir effects may be ignored.

Detecting the peak after compensation enables synchronization detectionwith reduced effects from multipath and correlation errors, and moreprecise detection than conventional synchronization detection.

Functional Structure of the Sync Detection Unit 23

Next is a detailed description of a functional structure of the syncdetection unit 23 of embodiment 1.

Detailed descriptions of functional units other than the sync detectionunit 23 have been omitted since they are the same as those used inconventional technology.

FIG. 2 shows the functional structure of the sync detection unit 23.

The sync detection unit 23 includes a correlation unit 231, a firstposition detection unit 232, a compensation unit 233, a second positiondetection unit 234 and a sync-detected signal generation unit 235.

Functions of these units are realized by software and hardware incooperation.

The correlation unit 231 cross-correlates a sequentially input symbolstring with a known symbol string (hereinafter, simply called areference symbol string).

FIG. 3 shows an exemplary structure of a correlation unit.

The correlation unit 231 shown in FIG. 3 uses a delay unit constitutedfrom a shift register or the like to delay symbols in a symbol string(i.e., the input signal) 1 symbol each, thereby shifting theverification position of the symbol string and the reference symbolstring input to the reference symbol string input unit, performs aconvolution operation, and sequentially outputs the resultingcorrelation values. Note that a detailed description of the structureshown in FIG. 3 has been omitted since it is the same as a conventionalcorrelation device.

In the present embodiment, a part of the training signal is used as thereference symbol string.

The first position detection unit 232 detects a position and value of acorrelation value viewed as the maximum or local maximum in the stringof correlation values (hereinafter, simply referred to as correlationvalue string) that is obtained as a result of the correlation unit 231cross-correlating the input symbol string and the reference symbolstring.

Note that the position mentioned above may be either an absoluteposition or a relative position, and the correlation value may also bean absolute value or a relative value.

FIG. 5 is a graph showing an exemplary correlation value string obtainedas a result of the correlation unit 231 correlating the input symbolstring and the reference symbol string.

When a single-carrier VSB modulated signal is received as a terrestrialbroadcast, symbol strings obtained from the received signal are oftendistorted due to the effects of white noise and multipath.

When taking one field-worth of correlation values between a symbolstring affected by white noise and multipath and a field sync symbolstring (i.e., reference symbol string), the resulting correlation valuestring will include more than one correlation value that can be viewedas the maximum or local maximum, which does not happen when taking onefield-worth of correlation values between a symbol string not affectedby white noise or multipath and a field synchronization symbol string(i.e., reference symbol string).

This phenomenon occurs due to the addition of error components frommultipath and white noise to correlation values at positions other thanthe true maximum (hereinafter, called correlation error values, andmentioned in detail later).

As shown in FIG. 5, the first position detection unit 232 viewscorrelation value=185 (S21) at T=9 and correlation value=169 (S22) atT=11 as the maximum and the local maximum, and detects T=9 and T=11.

Here, the maximum is the maximum absolute value, and the local maximumis the absolute value that results from a multipath interferencecomponent and white noise, and is smaller than the correlation valueviewed as the maximum.

As such, there may be two or more correlation values viewed as localmaxima. (Hereinafter, the maximum of the correlation values is called a“maximum correlation value,” and the local maximum of the correlationvalues is called a “local maximum correlation value.”)

Note that the first position detection unit 232 may detect the maximumor the local maximum before the correlation values become absolutevalues, or from correlation values raised to an arbitrary power insteadof absolute values.

The compensation unit 233 considers the correlation value at theposition detected by the first position detection unit 232 on thecorrelation value string to be the basis, and normalizes a predeterminednumber of correlation values at positions before and after the detectedposition. The compensation unit 233 then performs compensation byassociating the basis position of the normalized correlation valuestring with a maximum position of a prestored normalized correlationerror value string, and suppressing, from correlation values atpositions other than the basis position of the normalized correlationvalue string, correlation error values at positions on the correlationerror value string that correspond to the above positions.

Details of the compensation processing performed by the compensationunit 233 and correlation error value string are mentioned later.

Note that the compensation unit 233 may store a correlation error valuestring that has not been normalized, or may normalize the correlationerror value string by, for example, considering the maximum correlationvalue or local maximum correlation value detected by the first positiondetection unit 232 to be the basis. It is also possible for thecorrelation error value string to be obtained by an operation as needed,whereby the compensation unit 233 needs not prestore the correlationerror value string.

The second position detection unit 234 detects a single position of acorrelation value to be viewed as the maximum correlation value on thecorrelation value string compensated by the compensation unit 233.

Note that the second position detection unit 234 may detect at least onelocal maximum, or may detect a correlation value, or a position or valuerelative to a certain correlation value that has been considered to bethe basis.

The sync-detected signal generation unit 235 generates and outputs async-detected signal based on a position in the correlation value stringdetected by the second position detection unit 234.

Note that the sync-detected signal generation unit 235 may generate anarbitrary signal other than the synchronization signal, based on thecorrelation value or the position in the correlation value stringdetected by the second position detection unit 234.

Correlation Error Value String

Next is a description of the correlation error value string.

FIG. 6 is a graph showing a part of a correlation value string obtainedby considering 32 symbols in a PN511 to be a reference signal valuestring, and sequentially correlating a first field sync segment that hasnot been effected by white noise or multipath with the reference signalvalue string while shifting a verification position by one symbol from alead position of the first field sync segment.

As shown in FIG. 6, the maximum correlation value is at the 380thposition in the correlation value string, which has a value of 160.Correlation values at positions other than the maximum are calledcorrelation error values.

By using a part of the other know signal value string as the referencesignal value string for obtaining a correlation as mentioned above, thecorrelation value string obtained by correlating the signal value stringbefore and after the part and including the part with the referencesignal value string results in known values. In other words, thecompensation unit 233 can use the correlation error values as knownvalues.

Compensation Processing 1

Next is a description of compensation processing performed by thecompensation unit 233.

In order to facilitate understanding of processing content in thecompensation processing described below, the compensation unit 233 isassumed to prestore the correlation error value string shown in FIG. 7and FIG. 8, and only a correlation value string of the same length asthe stored correlation error value string is targeted for compensation.

FIG. 7 is a graph showing correlation error values from a correlationerror value string obtained by correlating a reference symbol string,which is apart of a training signal, with a part of a first field syncsegment, and performing normalization considering the maximumcorrelation value to be the basis, where the position of the maximumcorrelation value is t=0, and the graphed correlation errors values arein the range of t=−8 to t=8.

FIG. 8 shows the correlation error value string of FIG. 7 as a table.

First, when the first position detection unit 232 views correlationvalue=185 (S21) at T=9 in FIG. 5 as the maximum correlation value or thelocal maximum correlation value, the compensation unit 233 receives theposition information, considers correlation value=185 (S21) at T=9 to bethe basis, and normalizes the correlation value string.

FIG. 9A is a table showing part of the correlation value stringnormalized considering correlation value=185 (S21) at T=9 to be thebasis.

After normalizing the correlation value string, the compensation unit233 performs compensation by suppressing the correlation error values ofthe above correlation error value string from respective correlationvalues of the normalized correlation value string.

In other words, the compensation unit 233 performs compensation bysuppressing, from the correlation values on the normalized correlationvalue string shown in FIG. 9A, correlation error values that are on thecorrelation error value string shown in FIG. 8 and correspond to thepositions of the correlation values.

For example, correlation error value=−0.2 (S24) at t=−8 (S23) in thecorrelation error value string table shown in FIG. 8 is subtracted fromcorrelation value=−0.12 (S26) at t=−8 (S25) in the correlation valuestring table show in FIG. 9A.

As a result, the correlation value at t=−8 (S25) becomes−0.12−(−0.2)=0.08.

FIG. 9B is a table showing the correlation value string of FIG. 9A aftercompensation processing has been performed.

As is clear from the table shown in FIG. 9B, correlation value=−0.3(S40) at t=2 (S39) in the correlation error value string table of FIG. 8has been suppressed from correlation value=0.91 (S28) at t=2 (S27) ofFIG. 9A by the above compensation, thereby becoming 0.91−(−0.3)=1.21(S29), which is larger than correlation value=1.0 at t=0 (S30).

This shows that correlation value=169 (S22) at T=11 in FIG. 5 is largerthan correlation value=185 (S21) at T=9 after compensation, and in thiscase, the second position detection unit 234 views correlation value=169(S22) at T=11 in the compensated correlation value string as the maximumcorrelation value, and detects the position thereof.

Also, when the first position detection unit 232 views correlationvalue=169 (S22) at T=11 in FIG. 5 as the maximum correlation value orlocal maximum correlation value and detects the position thereof,compensation unit 233 may perform compensation processing afternormalizing the correlation value string considering correlationvalue=169 (S22) at T=11 to be the basis.

FIG. 10A is a table showing part of the correlation value stringnormalized considering correlation value=169 at T=11 to be the basis.

As is clear from the table shown in FIG. 1A, correlation value=1.09(S35) at t=−2 (S34) is larger than correlation value=1.0 (S33) at t=0(S32).

FIG. 10B is a table showing the correlation value string compensated bythe compensation unit 233.

As is clear from the table shown in FIG. 10B, there are no valuesgreater than correlation value=1.0 (S37) at t=0 (S36) in the compensatedcorrelation value string, and the pre-compensation correlationvalue=1.09 (S35) at t=−2 (S34) in FIG. 10A has been compensated to 0.79(S38) by suppressing correlation value=0.3 (S42) at t=−2 (S41) in thecorrelation error value string table shown in FIG. 8.

In this case, the second position detection unit 234 views thecorrelation value (S22) at T=11 in the compensated correlation valuestring output by the compensation unit 233 as the maximum, and detects aposition thereof.

Note that the second position detection unit 234 may view a correlationvalue at a position other than T=9 or T=11 as the maximum correlationvalue or local maximum correlation value, detect the position thereof,whereafter the above compensation processing is performed; or thecompensation processing may be repeatedly performed an arbitrary numberof times. Also, the compensation may be performed using an absolutevalue or value raised to an arbitrary power.

Compensation Processing 2

The present invention may perform compensation processing as describedbelow.

FIG. 11 is a flowchart for describing operations of compensationprocessing 2.

First, the first position detection unit 232 detects a first position ina correlation value string to be viewed as the maximum correlationvalue, and a second position in the correlation value string to beviewed as the local maximum correlation value (step S1).

Next, the compensation unit 233 judges whether to normalize thecorrelation value string considering the correlation value viewed as themaximum correlation value to be the basis (step S2). If the judgment isaffirmative (step S2:YES), the compensation unit 233 performscompensation by suppressing the correlation error value on theabove-mentioned correlation error value string at the positioncorresponding to the second position, from the correlation value at thesecond position in the normalized correlation value string (step S3).Processing then moves to step S4.

Also, if the judgment is negative (step S2:NO), processing moves to stepS4.

In step S4, the compensation unit 233 judges whether to normalize thecorrelation value string considering the correlation value viewed as thelocal maximum correlation value to be the basis (step S4).

If the judgment is affirmative (step S4:YES), the compensation unit 233performs compensation by suppressing the correlation error value on theabove-mentioned correlation error value string at the positioncorresponding to the first position, from the correlation value at thefirst position in the normalized correlation value string (step S5).Processing then returns to step S4.

Also, if the judgment is negative (step S4:NO), processing moves to stepS6.

Processing returns to step S1 if newly performing compensationprocessing (step S6:YES); otherwise, compensation processing ends (stepS6:NO).

The following is a specific description of compensation processing 2using FIG. 5, FIG. 8 to FIG. 10, and FIG. 12.

If the first position detection unit 232 detects correlation value=185(S21) at T=9 in FIG. 5 as the position of the maximum correlation value(i.e., the first position), and correlation value=169 (S21) at T=11 asthe position of the local maximum correlation value (i.e., the secondposition), the compensation unit 233 first judges whether to performnormalization considering correlation value=185 (S21) at T=9 (the firstposition) to be the basis.

If the compensation unit 233 normalizes the correlation value stringconsidering the first position to be the basis, the resultingcorrelation value string is as shown in the correlation value stringtable of FIG. 9A.

Next, the compensation unit 233 performs compensation by suppressingcorrelation error value=−0.3 (S40) at t=2 (S39) on the correlation errorvalue string in FIG. 8, from correlation value=0.91 (S28) at t=2 (S27)which is the posit-ion corresponding to T=11 (the second position) inthe correlation value string table in FIG. 9A.

FIG. 12A is a table showing a correlation value string resulting fromthe correlation value string in FIG. 9A being compensated bycompensation processing 2.

As is clear in FIG. 12A, the correlation value at t=2 (S43) is 1.21(S44), which is greater than the normalization basis value 1.0 (S45),that is, the correlation value viewed as the maximum correlation value.

The second position detection unit 234 therefore detects T=11 in FIG. 5as the position of the maximum correlation value.

Also, if the compensation unit 233 judges to perform normalizationconsidering the second position rather than the first position to be thebasis, the resulting correlation value string is as shown in thecorrelation value string table in FIG. 10A.

The compensation unit 233 performs compensation by suppressingcorrelation error value=0.3 (S42) at t=−2 (S41) on the correlation errorvalue string in FIG. 8, from correlation value=1.09 (S35) at t=−2 (S34)in the table shown in FIG. 10A, which corresponds to T=9 (the firstposition).

FIG. 12B is a table showing a correlation value string resulting fromthe correlation value string in FIG. 10A being compensated bycompensation processing 2.

As is clear in FIG. 12B, the correlation value at t=−2 (S46) is 0.79(S47), which is smaller than the normalization basis value 1.0 (S48),that is, the correlation value viewed as the maximum correlation value.

The second position detection unit 234 therefore detects T=11 as theposition of the maximum correlation value.

Note that it is assumed that two or more correlation values to be viewedas local maximum correlation values will be detected, and compensationmay be performed by normalizing the correlation value string with thecorrelation value viewed as the maximum correlation value, andsuppressing, from the correlation values at the plurality of secondpositions, the correlation error values at positions on the correlationerror value string corresponding to the second positions, ornormalization may be performed considering each of the local maximumcorrelation values to be the basis, and compensation may be performed bysuppressing correlation error values from corresponding correlationvalues at the first position or second positions corresponding to localmaximum correlation values other than the above-mentioned local maximumcorrelation values. Compensation may be performed by suppressingcorrelation values at positions other than the first or second position,and compensation processing may be repeatedly performed an arbitrarynumber of times. Furthermore, the correlation error value string may benormalized considering a correlation value at the detected first orsecond position to be the basis, without normalizing the correlationvalue string, or obtaining correlation error values to be used in thesuppression. Also, compensation may be performed using absolute valuesor values raised to an arbitrary power.

Compensation Processing 3

The present invention may perform the following compensation processing.

FIG. 13 is a flowchart for describing operations of compensationprocessing 3.

The maximum correlation value and local maximum correlation value are asdescribed in the above compensation processing 2.

First, the first position detection unit 232 detects a first position ina correlation value string to be viewed as the maximum correlation valueand a second position in the correlation value string to be viewed asthe local maximum correlation value (step S11). Note that the firstposition detection unit 232 may detect two or more local maximumcorrelation values.

Next, if the first position is considered to be the basis position, thecompensation unit 233 specifies a correlation error value (correlationerror value A) at a position in the above-mentioned correlation errorvalue string that corresponds to the second position in the correlationvalue string (step S12).

If the second position is considered to be the basis position, thecompensation unit 233 then specifies a correlation error value(correlation error value B) at a position in the correlation error valuestring corresponding to the first position in the correlation valuestring (step S13).

The compensation unit 233 obtains a composite correlation error value bysubtracting the correlation error value B specified in step S13 from thecorrelation error value A specified in step S12 (step S14).

The compensation unit 233 performs compensation by suppressing thecomposite correlation error value obtained in step S14 from thecorrelation value string normalized considering the correlation valueviewed as the maximum correlation value to be the basis (step S15).

Processing returns to step S1 if compensation processing is to be newlyperformed after step S15 (step S16:YES); otherwise (step S16:NO),compensation processing ends.

Next is a specific description using FIG. 5, FIG. 8, FIG. 9 and FIG. 14.

If the positions at correlation value=185 (S21) at T=9 and correlationvalue=169 (S22) at T=11 in FIG. 5 are detected as the maximumcorrelation value and local maximum correlation value (i.e., the firstposition and second position) respectively, the compensation unit 233specifies the correlation error value A at the position in thecorrelation error value string shown in FIG. 8 corresponding to T=11(the second position) if T=9 (the first position) is considered to bethe basis position. In other words, the correlation error value A iscorrelation error value=−0.3 (S40) at t=2 (S30) in the correlation errorvalue string shown in FIG. 8.

Also, the compensation unit 233 specifies the correlation error value Bat the position in the correlation error value string shown in FIG. 8corresponding to T=9 (the first position) if T=11 (the second position)is considered to be the basis position. In other words, the correlationerror value B is correlation error value=0.3 (S42) at t=−2 (S41) in thecorrelation error value string shown in FIG. 8. Next, the compensationunit 233 obtains the composite correlation error value. Since thecomposite correlation error value equals the correlation error value Aminus the correlation error value B, the composition correlation errorvalue is −0.3−(0.3)=−0.6.

The compensation unit 233 then normalizes the correlation value stringconsidering the correlation value at the first position to be the basis.FIG. 9A shows the correlation value string normalized considering thecorrelation value at T=9 to be the basis. The compensation unit 233 thenperforms compensation by suppressing the composite correlation errorvalue from correlation values at positions other than the basis position(t=0) in the normalized correlation value string shown in FIG. 9A.

FIG. 14 is a table showing the correlation value string shown in FIG. 9Aafter having been compensated by compensation processing.

As a result, the correlation value at t=2 (S49) in FIG. 14 is0.91−(−0.6)=1.51 (S50), which is the largest value on the compensatedcorrelation value string.

The second position detection unit 234 therefore detects T=11, which isthe position at t=2 (S49), as the position of the maximum correlationvalue.

Note that the compensation unit 233 may perform compensation byperforming normalization considering at least one detected secondposition to be the basis and suppressing the obtained compositecorrelation error value from the correlation value string, may obtainthe composite error value using two or more correlation error valuescorresponding to the plurality of second positions, may performcompensation by suppressing a composite correlation error value fromcorresponding correlation values other than the first and secondpositions, and may repeatedly perform compensation processing anarbitrary number of times. Furthermore, the compensation unit 233 mayperform compensation by normalizing the correlation error value stringconsidering the at least one correlation value at the detected first andsecond positions to be the basis without normalizing the correlationvalue string, and obtaining a composite correlation error value to beused in the suppression. Also, the compensation unit 233 may performcompensation using absolute values or values raised to an arbitrarypower.

Variation 1

The sync detection unit of the present invention may have the followingstructure.

FIG. 15 shows a functional structure of the sync detection unit ofvariation 1.

Function units of a sync detection unit 23A in FIG. 15 that are the sameas in the above-mentioned sync detection unit 23 have been given thesame characters, and descriptions thereof have been omitted.

The sync detection unit 23A differs from the sync detection unit 23 withrespect to the inclusion of a second correlation unit 236, a polaritydetection unit 237 and a field number signal generation unit 238, andfunctions of the a compensation unit 233A differ somewhat from thecompensation unit 233.

The second correlation unit 236 may have the same structure as thecorrelation unit 231 shown in FIG. 3 and FIG. 15, and uses a part of asecond PN63 symbol string as the reference symbol string forcorrelation. Note that the second correlation unit 236 may output onlycorrelation values necessary for detecting polarity, may output anyvalue at other times, as well as may temporarily stop outputting values.

The polarity detection unit 237 outputs a polarity specified from aposition viewed as the maximum in the correlation value string outputfrom the second correlation unit 236. If the polarity of the second PN63symbol string is inverse of the polarity of the first and third PN63symbol strings, the second PN63 symbol string can be identified as beingin the second field.

Note that the polarity detection unit 237 may use only a portion of thecorrelation that is necessary to detect polarity, and at this time, mayuse the position of the correlation value detected by the first positiondetection unit 232 or the second position detection unit 234 consideredto be the maximum.

The compensation unit 233A only differs from the compensation unit 233of embodiment 1 with respect to performing compensation processing usingthe polarity output by the polarity detection unit 237, and all otherfunctions are the same.

The compensation unit 233A stores a correlation error value stringobtained by cross-correlating a known symbol string not affected bywhite noise or multipath and including from the PN511 symbol string tothe third PN63 symbol string, with a reference symbol string which is apart of the PN511 symbol string.

There are two patterns for the second PN63 symbol string,polarity-reversed and not, and the compensation unit 233A stores acorrelation error value string corresponding to each of these twopatterns. More precisely, the compensation unit 233A stores at least apart of these correlation error value strings normalized with arespective maximum.

The compensation unit 233A also obtains the polarity of the second PN63portion detected by the polarity detection unit 237, judges which of theerror value string patterns to use for performing compensation, andperforms compensation processing.

Note that the correlation error value strings can be obtained as-neededby an operation, and in this case, the compensation unit 233A may notstore correlation error value string in advances, or may store onepattern of correlation error value string and a difference between thispattern and the other pattern.

The field number signal generation unit 238 generates and outputs afield number signal based on the polarity output by the polaritydetection unit 237. Note that the field number signal generation unit238 may be able to output any signal.

Using the sync detection unit 23A of variation 1 enables performingcompensation processing using longer correlation error value stringsthan when using the above-mentioned sync detection unit 23, therebyexpanding the compensatable range for distorted channel response andenabling high-precision estimation for channel response pertaining tolonger periods of time.

Variation 2

The sync detection unit of the present invention may have the followingstructure.

FIG. 16 shows a functional structure of the sync detection unit ofvariation 2.

Function units of a sync detection unit 23B in FIG. 16 that are the sameas in the above-mentioned sync detection unit 23 and the sync detectionunit 23A described in variation 1 have been given the same characters,and descriptions thereof have been omitted.

The sync detection unit 23B differs from the sync detection unit 23A ofvariation 1 with respect to the inclusion of a mode detection unit 239and a VSB mode signal generation unit 240, and functions of acompensation unit 233B differ somewhat from the compensation unit 233.

The mode detection unit 239 detects a VSB mode symbol included in theinput signal, with use of a reference symbol string which is a part of aVSB mode symbol string.

Note that the mode detection unit 239 may select, from the input signal,only a portion necessary for detecting the mode, and here, may useposition information of the correlation value detected as the maximum bythe first position detection unit 232 or the second position detectionunit 234.

The compensation unit 233B only differs from the compensation unit 233Aof variation 1 with respect to performing compensation processing usinga known VSB mode symbol string that specifies the VSB mode detected bythe mode detection unit 239, whereby all other functions are the same.

The compensation unit 233B stores a correlation error value stringobtained by cross-correlating a known symbol string not affected bywhite noise or multipath and including from the PN511 symbol string tothe VSB mode symbol string, and a part of the PN511 symbol string.

As mentioned in variation 1, there are two patterns for the second PN63symbol string, polarity-reversed and not, and there are at most fivetypes of VSB modes, whereby the sync detection unit of the presentinvention stores a total of 10 (2×5=10) correlation error value stringscorresponding to these patterns. More precisely, the sync detection unitstores at least a part of these correlation error value stringsnormalized with a respective maximum.

The compensation unit 233B also obtains the polarity of the second PN63portion detected by the polarity detection unit 237 and the VSB modedetected by the mode detection unit 239, judges which of the correlationerror value string patterns to use for performing compensation, andperforms compensation processing.

Note that variation 2 may be applied to embodiment 1 as well asvariation 1, the correlation error value strings can be obtainedas-needed by an operation, and in this case, the compensation unit 233Bmay not store correlation error value strings in advance, or may storeone pattern of correlation error value string and differences betweenthis pattern and the other patterns.

The VSB mode signal generation unit 240 generates and outputs a VSB modesignal based on the VSB mode symbol string detected by the modedetection unit 239. Note that the VSB mode signal generation unit 240may be able to output any signal.

Using the sync detection unit 23B of variation 2 enables performingcompensation processing us linger correlation error value strings thanwith use of the above-mentioned sync detection units 23 and 23A, therebyexpanding the compensatable range for distorted channel response andenabling high-precision estimation for channel response pertaining tolonger periods of time.

Embodiment 2

The following describes a signal detection device of embodiment 2.

In the present embodiment, the signal detection device of the presentinvention is used as the mode detection unit described in variation 2 ofthe above-mentioned embodiment 1.

One method of conventional VSB mode detection uses two levels ofhard-decided values. The VSB mode detection method disclosed in U.S.Pat. No. 5,745,528 is one such example.

Even if the input signal is distorted by white noise and multipath,using the mode detection unit of the present invention enables moreaccurate VSB mode detection than using hard-decision, which is theconventional VSB mode detection method.

FIG. 17 shows a functional structure of the mode detection unit.

A mode detection unit 239A includes a third correlation unit 501 and amode specification unit 502 as function units.

The third correlation unit 501 cross-correlates a sequentially inputsymbol string and a VSB mode symbol string that identifies VSB modes ofthe ATSC system.

Note that a position of the VSB mode symbol string may be specifiedbased on a maximum position detected by the first position detectionunit 232 or the second position detection unit 234 of theabove-mentioned embodiment 1.

FIG. 18 is a table showing 24-bit data of VSB modes in the ATSC system.A bit in FIG. 18 is one symbol, where 1 represents the level “+5” and 0represents the level “−5”.

There are five types of VSB modes, namely 2-VSB, 4-VSB, 8-VSB, 16-VSBand TC 8-VSB.

The mode specification unit 502 specifies, from the correlation resultoutput by the third correlation unit 501 with respect to the VSB modesymbol strings, a VSB mode symbol string with the maximum, and outputsthe specified VSB mode symbol string with the maximum to the VSB modesignal generation unit 240.

According to the above structure, even if the received signal isdistorted by white noise and multipath, the mode specification unit 502can specify, from the correlation of the sequentially input symbolstrings and the VSB mode symbol strings identifying VSB modes in theATSC system, the VSB mode symbol string with the maximum as the VSB modeof the input symbol string, thereby enabling more accurate VSB modedetection than by hard-decision, which is the conventional method of VSBmode detection.

Variation 3

The mode detection unit of the present invention may also have thefollowing structure.

FIG. 19 shows a functional structure of a mode detection unit 239B ofvariation 3.

The mode detection unit 239B includes a third correlation unit 501, acumulative addition unit 503 and a mode specification unit 504.

The third correlation unit 501 is the same as described above.

The cumulative addition unit 503 obtains correlations between the inputsymbol strings and VSB mode symbol strings for only a predeterminednumber of fields, and cumulatively adds the obtained correlation valuesto each of the VSB mode symbol strings.

The mode specification unit 504 specifies the VSB mode symbol stringwith the largest value added by the cumulative addition unit 503, andoutputs the specified VSB mode symbol string to the VSB mode signalgeneration unit 240.

According to the structure in variation 3, cumulatively addingcorrelation values of VSB modes for only a predetermined number offields enables accurate VSB mode detection even if there is a momentarygeneration of a very large amount of white noise or the like.

Variation 4

The mode detection unit of the present invention may also have thefollowing structure.

FIG. 20 shows a functional structure of a mode detection unit 239C ofvariation 4.

The mode detection unit 239C includes a distance calculation unit 601, acumulative addition unit 602 and a mode specification unit 603.

The distance calculation unit 601 specifies a section position of a VSBmode symbol string in an input symbol string, based on the positiondetection by the first position detection unit 232 or second positiondetection unit 234 described in embodiment 1, and calculates, as adistance for each VSB mode, a level difference between at least onesymbol value in the specified section and a corresponding symbol valueon each known VSB module symbol string.

The cumulative addition unit 602 cumulatively adds the distance obtainedfor each VSB mode by the distance calculation unit 601.

The mode specification unit 603 specifies the VSB mode symbol stringwith the lowest value added by the cumulative addition unit 602, andoutputs the specified VSB mode symbol string to the VSB mode signalgeneration unit 240.

According to the structure in variation 4, it is possible to accuratelyperform VSB mode detection even if there is white noise and multipathsince the distance from the VSB mode symbol can be cumulatively addedusing the signal before hard-decision.

Also, the mode detection unit 239C may have a structure in which thecumulative addition unit 602 cumulatively adds distances from VSB modesymbols for only a predetermined number of fields, and the addeddistances are output to the mode specification unit 603.

According to this structure, cumulatively adding distances with respectto VSB mode symbols for only a predetermined number of fields enablesaccurate VSB mode detection even if there is a momentary generation: ofa very large amount of white noise or the like.

Supplementary Remarks

Note that the present invention is of course not limited to the contentdescribed in the above embodiments. In other words:

(1) The sync detection unit of embodiment 1 and variations 1 and 2 maydetect a reference symbol string from any signal after modulation, andmay estimate channel response.

(2) The correlation unit 231 of embodiment 1 may select only a portionof the input signal necessary for correlation, and cross-correlate theselected portion with the reference symbol string.

(3) The correlation value positions detected by the first positiondetection unit 232 and the second position detection unit 234 describedin embodiment 1 may be indicated as relative positions when apredetermined position has been considered to be the basis.

(4) Unless performing compensation by suppressing correlation errorvalues from correlation values, the compensation units 233, 233A and233B described in embodiment 1 and variations 1 and 2 may only normalizethe correlation value string.

(5) The compensation unit 233 described in embodiment 1 may consider allcorrelation values other than the maximum to be correlation errorvalues, and perform compensation by setting at least a part of positionsof the correlation error values that require compensation as apredetermined value such as 0.

(6) The compensation unit 233 described in embodiment 1 may, with theaim of suppressing errors in the correlation value string down to, forexample, a predetermined basis value of an error etc. included in apredetermined local maximum, perform compensation processing byreplacing the portion considered to be the maximum with one of severalpredetermined local maxima.

(7) Given that the power levels of a reception signal transmitted on adirect path and a reception signal transmitted on a reflex path areoften different, the compensation unit 233 described in embodiment 1 mayconsider both reception signals to have the same power level and storeor calculate in advance respective correlation error value strings or acomposited correlation error value string in order to facilitatecompensation.

(8) In order to obtain more reliable output, the second positiondetection unit 234 described in embodiment 1 may accumulate two or moredetected maxima, and output at least one of a most accumulated position,a position of a maximum for a relative position, or a relative position,or an average proportional value of the correlation value or an averageproportional value of the proportional correlation value; or in order toavoid erroneous variations due to noise etc. on the channel, may outputat least one of a pre-variation position, relative position, correlationvalue, or relative correlation value until the number of times theposition has changed reaches a predetermined count.

(9) The sync-detected signal generation unit 235 described in embodiment1 may generate and output any signal such as a signal specifying aposition in a correlation value string detected by the second positiondetection unit 234 or a corresponding section.

(10) The sync-detected signal generation unit 235 described inembodiment 1 can also output any signal using input, and, when aposition output by the second position detection unit 234 changes, mayoutput an amount of the change in the position to notify the change toother units.

(11) If a recommendation symbol string such as PN63, a symbol string tobe used in a future expanded system, or the like is included in at leasta part of a reserved symbol string following the VSB mode symbol string,the mode detection unit 239 described in variation 2 may detect at leasta part of this symbol string, and the detection may be used by thecompensation unit 233B.

In this case, at least the part of the detected reserved symbol stringis added to the known symbol string, thereby obtaining a longercorrelation error value string and enabling the compensation unit 233Bto perform compensation on a longer correlation value string.

(12) Although the third correlation unit 501 of embodiment 2 andvariation 3 was described as having a structure that cross-correlatesall VSB mode symbol strings and the input symbol string, across-correlation may not be taken with respect to a common portion ofsymbols string of all VSB modes.

(13) The third correlation unit 501 of embodiment 2 and variation 3 neednot necessarily cross-correlate all VSB mode symbol strings with theinput symbol string, and if, for example, a cross-correlation is onlyrequired with two types of VSB modes, only the portion of one VSB modesymbol string that differs from the other VSB mode symbol string may becross-correlated. Only a single correlation device is necessary sincethe cross-correlation result with the other VSB mode symbol string canbe obtained by sign-inversion.

(14) The third correlation unit 501 described in embodiment 2 andvariation 3, the cumulative addition unit 503 of variation 3, and thecumulative addition unit 602 of variation 4 may normalize thecorrelation values. One example of the normalization method involvessubtracting the lowest correlation value from each of the correlationvalues. This reduces the bit-width required for the correlation values.

(15) The third correlation unit 501 described in embodiment 2 andvariation 3 and the distance calculation unit 601 described in variation4 may calculate correlations after lowering the precision of the inputsymbol string, that is, the bit-width. This enables the reduction of thecircuitry scale for correlation operations or distance calculations.

(16) The third correlation unit 501 described in embodiment 2 andvariation 3 may calculate correlation values by taking an absolute valueof the input symbol string, or the mode specification unit 502 mayinstead detect the maximum with respect to the absolute value of thecorrelation value.

This enables the maximum to be detected even if 180 degree phaseuncertainty exists in the input signal.

(17) The cumulative addition unit 503 described in variation 3 and thecumulative addition unit 602 described in variation 4 may average acumulative correlation value or cumulative distance in field units andoutput the averaged cumulative correlation value or cumulative distance.

As a result, the accuracy of VSB mode detection is even higher. Slidingaverage can be used in the average processing.

(18) The cumulative addition unit 602 described in variation 4cumulatively adds distances with respect to the VSB mode symbol strings.However, the cumulative addition unit 602 may not perform cumulativeaddition with respect to, for example, symbols that are common symbolstring candidates for all VSB modes. In this case, the differencesbetween cumulatively added values between VSB modes are the same as theabove examples, and the performance of VSB mode detection is the same.

(19) Compensation processing can be at least temporarily stopped ifthere is no need for compensation in the compensation units 233, 233Aand 233B described in embodiment 1.

(20) Given that it is conceivable for the local maxima and positionsversus the maximum in the output signal output from the compensationunits 233, 233A and 233B described in embodiment 1 to indicate valuesand delay times of a signal transmitted over a reflex pathway versus asignal transmitted over a direct pathway, the local maxima and positionsthereof can be used as impulse responses of the distorted channel. Forexample, they can be used in coefficient generation of the equalizationunit 24 shown in FIG. 1, can be monitored as channel response, and canbe used in a spectrum conversion unit etc. (not depicted) for conversionto spectrum using Fourier transform or the like.

(21) In order to increase tolerance for noise on channels, theabove-mentioned correlation unit 231, first position detection unit 232,second position detection unit 234, second correlation unit 236 andpolarity detection unit 237 may perform processing after considering apredetermined section from among at least a portion composed of at leastone group in the input signal to be a unit and obtaining a proportionalvalue that has been averaged per position of two or more units. Also, asection of at least a portion composed of at least one group on theprocessing results may be considered to be a unit, and a proportionalvalue that has been averaged per position of two or more units may beobtained and output.

(22) Output of the above-mentioned compensation units 233, 233A and 233Bmay be pre-compensation correlation output. Also, such output may beoutput that has been averaged per field unit, and sliding average may beused in the average processing.

(23) In embodiment 1, the length of the reference signal used forcorrelation when generating output from the compensation units 233, 233Aand 233B may be different from the length of the reference signal usedfor correlation when generating correlation output from the correlationunit 231 to the first position detection unit 232, and the compensationunits may be provided with a correlation unit other than the correlationunit 231 for output signals.

Furthermore, the correlation values obtained by using a portion of thesignal value string input to the correlation unit 231 may be set as theoutput signal. Alternatively, the correlation value string output fromthe correlation unit 231 may also be used as the output signal, and thecorrelation values obtained using a portion of the signal value stringinput to the correlation unit 231 may be input to the first positiondetection unit 232.

(24) The sync detection units 23, 23A and 23B described in embodiment 1may detect either a field synchronization symbol or a segmentsynchronization symbol first, and may use either detection result.

(25) The reference symbol string described in embodiments 1 and 2 is notlimited to a portion of the segment sync, PN511, PN63, VSB mode symbolstring or reserved symbol string. In other words, any complex signalother than a VSB signal may be used as the input symbol string. Also,the signal targeted for detection is not limited to a synchronizationsignal, but rather may be, for example, any signal such as an acyclicsignal.

(26) It may be possible to receive output from another unit of thereception device shown in FIG. 1 to increase the length of the knownsymbol string. In this case, for example, at least one input may beadded to the compensation units 233, 233A and 233B to increase thenumber of stored correlation error values.

(27) The above-mentioned functional units may have structures that use areduced operation precision or polarity of the input signal or outputsignal. For example, the functional units may use-values raised to anarbitrary power.

(28) In embodiment 1, when the position information output by the secondposition detection unit 234 changes, the sync-detected signal generationunit 235 may additionally output the variation of the position shown inFIG. 4.

(29) Although a position in the VSB mode symbol string may be specifiedbased on the position information output by the first position detectionunit 232 or the second position detection unit 234 in embodiment 2, aposition in the VSB mode symbol string may be specified by includinganother functional-unit that generates an information signal equivalentto the position information output by the first position detection unit232 or second position detection unit 234.

(30) The signal detection device of embodiment 2 is described as a modedetection device that detects, but is not limited to, an ATSC system VSBmode, and can be applied to cases of signals of any system if thesignals include a known signal for mode specification.

(31) Although described as a mode detection device that detects any of2-VSB, 4-VSB, 8-VSB, 16-VSB and TC 8-VSB modes in embodiment 2, thesignal detection device pertaining to the present invention may performVSB mode detection using only the two modes 16-VSB and TC 8-VSB ascandidates since operation provisions for U.S. DTV specify the operationof only these two modes. Also, the mode candidates need not be limitedto the aforementioned.

(32) Although the signal detection device of embodiment 2 is describedas detecting a VSB mode symbol string in embodiment 2, if, for example,there are two or more known symbol string candidates in the reservedarea of the field sync segment shown in FIG. 4, the signal detectiondevice may, in parallel with VSB mode detection, detect the most likelycandidate (mode) in the reserved area. This can be realized by providinga set of all the units shown in embodiment 2 for each of the candidatesto be detected.

(33) In order to manage positions and processing times of the functionalunits, the signal detection device described in the embodiments may beprovided with at least one time measuring unit for using a counter etc.outputting time information to obtain an elapsed time etc. from apredetermined time, and the output of the time measuring unit may beinput to and used by at least one of the functional units.

(34) An aim of the present invention may be realized by storing signaldetection processing performed by the signal detection device describedin the embodiments as a computer program in memory, and causing thesignal detection processing to be performed with use of a CPU or thelike. In other words, the present invention may be such a computerprogram. Also, the present invention may be digital signals representingthe computer program.

(35) Also, the present invention may be a computer-readable recordingmedium such as a flexible disk, a hard disk, a CD-ROM, an MO, a DVD, aDVD-ROM, a DVD-RAM, a BD (Blu-ray Disc), or a semiconductor memory onwhich the computer programs or the digital signals are recorded.

(36) The present invention may be a signal detection method includingthe operations of the above-mentioned compensation processing (e.g.,operations shown in FIG. 11 and FIG. 13).

(37) The present invention may be a signal detection circuit constitutedfrom circuits that perform processing equivalent to the functional unitsconstituting the above-mentioned signal detection device.

(38) In embodiment 1, the front-end unit 2 and the back-end unit 3 mayeach be made into a single and separate chip, or may be made into asingle chip including a portion or all portions thereof.

IC or an LSI depending on the integration degree of the elements.

Also, a special purpose circuit, general purpose processor, acombination thereof etc., or an FPGA (Field Programmable Gate Array)having a modifiable architecture, a reconfigurable processor, acombination thereof etc. may be used as an integrated circuit device,and moreover, if another device substituting a semiconductor integratedcircuit is proposed according to technological advances, such a devicemay be used as the integrated circuit device. One such example is anintegrated circuit using biotechnology. Also, the signals targeted forprocessing may be not only electrical signals, but any signal such asoptical signals, magnetic signals, or a combination thereof.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a digital broadcast receptiondevice, a relaying device, a wireless or wire communication device, ameasuring device, or an integrated circuit, program etc. having suchconstituent elements.

1. A signal detection device, comprising: a correlation unit operable tooutput a correlation value string based on a result of cross-correlating(i) a reference signal value string included in an input signal valuestring and (ii) signal value strings that are obtained by shifting acertain signal value string one by one in order of the input signalvalue string and that correspond in length to the reference signal valuestring; and a compensation unit operable to perform compensation byobtaining a correlation error of at least one of the output correlationvalues and suppressing the correlation error from the at least onecorrelation value.
 2. The signal detection device of claim 1, furthercomprising: a first position detection unit operable to detect a firstposition in the correlation value string output by the correlation unit,the first position being based on a position of a correlation valueviewed as a maximum or a local maximum, wherein the compensation unitperforms the compensation by obtaining the correlation error of thecorrelation value at at least one position other than the first positiondetected by the first position detection unit, and suppressing thecorrelation error from the at least one correlation value.
 3. The signaldetection device of claim 2, further comprising: a second positiondetection unit operable to detect a second position in the correlationvalue string compensated by the compensation unit, the second positionbeing based on a position of a correlation value viewed as a maximum onthe compensated correlation value string.
 4. The signal detection deviceof claim 2, wherein the compensation unit performs the compensation byassociating the first position detected by the first position detectionunit and a position of a maximum on a correlation error value stringthat is based on a result of cross-correlating the reference signalvalue string and signal value strings which are obtained by shifting acertain signal value string one by one in order of a known signal valuestring including the reference signal value string and which correspondin length to the reference signal value string, and suppressing, basedon a correlation error value at a position in the correlation errorvalue string corresponding to a second position other than the firstposition, the correlation error from a correlation value at the secondposition.
 5. The signal detection device of claim 1, wherein a secondreference signal value string specifying a polarity is included in theinput signal value string, the signal detection device furthercomprises: a second correlation unit operable to output a secondcorrelation value string based on a result of cross-correlating thesecond reference signal value string and signal value strings that areobtained by shifting a certain signal value string one by one in orderof the input signal value string and that correspond in length to thesecond reference signal value string; and a polarity detection unitoperable to output a polarity that is specified based on a position of acorrelation value viewed as a maximum or a local maximum on the secondcorrelation value string output by the second correlation unit, and thecompensation unit performs the compensation based on the polarityspecified by the polarity detection unit and the correlation error. 6.The signal detection device of claim 1, wherein a third reference signalvalue string specifying a signal mode of an input signal is included inthe input signal value string, the signal detection device furthercomprises: a mode detection unit operable to detect the third referencesignal value string based on the input signal value string, and thecompensation unit performs the compensation based on a signal modedetected by the mode detection unit and the correlation error.
 7. Thesignal detection device of claim 2, wherein the first position detectionunit detects a maximum position that is a position corresponding to acorrelation value viewed as the maximum on the correlation value string,and a local maximum position that is a position corresponding to acorrelation value viewed as the local maximum on the correlation valuestring, and the compensation unit performs the compensation by one ofassociating the local maximum position and a position of a maximum on acorrelation error value string that is based on a result ofcross-correlating the reference signal value string and signal valuestrings which are obtained by shifting a certain signal value string oneby one in order of a known signal value string including the referencesignal value string and which correspond in length to the referencesignal value string, obtaining a correlation error value on thecorrelation error value string at a position corresponding to themaximum position, and suppressing, based on the correlation error value,a correlation error from the correlation value at the maximum position,and associating the maximum position and a position of a maximum on thecorrelation error value string, obtaining a correlation error value onthe correlation error value string at a position corresponding to thelocal maximum position, and suppressing, based on the correlation errorvalue, a correlation error from the correlation value at the localmaximum position.
 8. The signal detection device of claim 2, wherein thefirst position detection unit detects a maximum position that is aposition in the correlation value string which corresponds to acorrelation value viewed as the maximum, and a local maximum positionthat is a position in the correlation value string which corresponds toa correlation value viewed as the local maximum, and the compensationunit performs the compensation by associating the maximum position and aposition of a maximum on a correlation error value string that is basedon a result of cross-correlating the reference signal value string andsignal value strings which are obtained by shifting a certain signalvalue string one by one in order of a known signal value stringincluding the reference signal value string and which correspond inlength to the reference signal value string, obtaining a firstcorrelation error value on the correlation error value string at aposition corresponding to the local maximum position, associating thelocal maximum position and the position of the maximum on thecorrelation error value string, obtaining a second correlation errorvalue on the correlation error value string at a position correspondingto the maximum position, and one of suppressing, based on a firstcomposite correlation error value obtained by subtracting the secondcorrelation error value from the first correlation error value, acorrelation error from the correlation value at the local maximumposition, and suppressing, based on a second composite correlation errorvalue obtained by subtracting the first correlation error value from thesecond correlation error value, a correlation error from the correlationvalue at the maximum position or the local maximum position.
 9. Thesignal detection device of claim 1, wherein the compensation unitoutputs a value that is based on a compensated correlation value stringto at least one of an equalization unit, a spectrum conversion unit, anda channel response measuring unit.
 10. The signal detection device ofclaim 3, wherein if a currently detected position differs from apreviously detected position, the second position detection unit outputsan amount of change therebetween.
 11. A signal detection circuit,comprising: a correlation circuit operable to output a correlation valuestring based on a result of cross-correlating (i) a reference signalvalue string included in an input signal value string and (ii) signalvalue strings that are obtained by shifting a certain signal valuestring one by one in order of the input signal value string and thatcorrespond in length to the reference signal value string; and acompensation circuit operable to perform compensation by obtaining acorrelation error of at least one of the output correlation values andsuppressing the correlation error from the at least one correlationvalue.
 12. The signal detection circuit of claim 11, further comprising:a first position detection circuit operable to detect a first positionin the correlation value string output by the correlation circuit, thefirst position being based on a position of a correlation value viewedas a maximum or a local maximum, wherein the compensation circuitperforms the compensation by obtaining the correlation error of thecorrelation value at at least one position other than the first positiondetected by the first position detection circuit, and suppressing thecorrelation error from the at least one correlation value.
 13. Thesignal detection circuit of claim 12, further comprising: a secondposition detection circuit operable to detect a second position in thecorrelation value string compensated by the compensation circuit, thesecond position being based on a position of a correlation value viewedas a maximum on the compensated correlation value-string.
 14. The signaldetection circuit of claim 11, wherein the compensation circuit performsthe compensation by associating the first position detected by the firstposition detection circuit and a position of a maximum on a correlationerror value string that is based on a result of cross-correlating thereference signal value string and signal value strings which areobtained by shifting a certain signal value string one by one in orderof a known signal value string including the reference signal valuestring and which correspond in length to the reference signal valuestring, and suppressing, based on a correlation error value at aposition in the correlation error value string corresponding to a secondposition other than the first position, the correlation error from acorrelation value at the second position.
 15. The signal detectioncircuit of claim 11, wherein a second reference signal value stringspecifying a polarity is included in the input signal value string, thesignal detection circuit further comprises: a second correlation circuitoperable to output a second correlation value string based on a resultof cross-correlating the second reference signal value string and signalvalue strings that are obtained by shifting a certain signal valuestring one by one in order of the input signal value string and thatcorrespond in length to the second reference signal value string; and apolarity detection circuit operable to output a polarity that isspecified based on a position of a correlation value viewed as a maximumor a local maximum on the second correlation value string output by thesecond correlation circuit, and the compensation circuit performs thecompensation based on the polarity specified by the polarity detectioncircuit and the correlation error.
 16. The signal detection circuit ofclaim 11, wherein a third reference signal value string specifying asignal mode of an input signal is included in the input signal valuestring, the signal detection circuit further comprises: a mode detectioncircuit operable to detect the third reference signal value string basedon the input signal value string, and the compensation circuit performsthe compensation based on a signal mode detected by the mode detectioncircuit and the correlation error.
 17. The signal detection circuit ofclaim 12, wherein the first position detection circuit detects a maximumposition that is a position corresponding to a correlation value viewedas the maximum on the correlation value string, and a local maximumposition that is a position corresponding to a correlation value viewedas the local maximum on the correlation value string, and thecompensation circuit performs the compensation by one of associating thelocal maximum position and a position of a maximum on a correlationerror value string that is based on a result of cross-correlating thereference signal value string and signal value strings which areobtained by shifting a certain signal value string one by one in orderof a known signal value string including the reference signal valuestring and which correspond in length to the reference signal valuestring, obtaining a correlation error value on the correlation errorvalue string at a position corresponding to the maximum position, andsuppressing, based on the correlation error value, a correlation errorfrom the correlation value at the maximum position, and associating themaximum position and a position of a maximum on the correlation errorvalue string, obtaining a correlation error value on the correlationerror value string at a position corresponding to the local maximumposition, and suppressing, based on the correlation error value, acorrelation error from the correlation value at the local maximumposition.
 18. The signal detection circuit of claim 12, wherein thefirst position detection circuit detects a maximum position that is aposition in the correlation value string which corresponds to acorrelation value viewed as the maximum, and a local maximum positionthat is a position in the correlation value string which corresponds toa correlation value viewed as the local maximum, and the compensationcircuit performs the compensation by associating the maximum positionand a position of a maximum on a correlation error value string that isbased on a result of cross-correlating the reference signal value stringand signal value strings which are obtained by shifting a certain signalvalue string one by one in order of a known signal value stringincluding the reference signal value string and which correspond inlength to the reference signal value string, obtaining a firstcorrelation error value on the correlation error value string at aposition corresponding to the local maximum position, associating thelocal maximum position and the position of the maximum on thecorrelation error value string, obtaining a second correlation errorvalue on the correlation error value string at a position correspondingto the maximum position, and one of suppressing, based on a firstcomposite correlation error value obtained by subtracting the secondcorrelation error value from the first correlation error value, acorrelation error from the correlation value at the local maximumposition, and suppressing, based on a second composite correlation errorvalue obtained by subtracting the first correlation error value from thesecond correlation error value, a correlation error from the correlationvalue at the maximum position or the local maximum position.
 19. Thesignal detection circuit of claim 11, wherein the compensation circuitoutputs a value that is based on a compensated correlation value stringto at least one of an equalization circuit, a spectrum conversioncircuit, and a channel response measuring circuit.
 20. The signaldetection circuit of claim 13, wherein if a currently detected positiondiffers from a previously detected position, the second positiondetection circuit outputs an amount of change therebetween.
 21. Thesignal detection circuit of claim 16, further comprising: a firstposition detection circuit operable to detect a first position in thecorrelation value string output by the correlation circuit, the firstposition being based on a position of a correlation value viewed as amaximum or a local maximum; and a second position detection circuitoperable to detect a second position in the correlation value stringcompensated by the compensation circuit, the second position being basedon a position of a correlation value viewed as a maximum on thecompensated correlation value string, wherein the mode detection circuitcomprises: a third correlation circuit operable to specify a positionsection of a mode signal value string in the input signal with use ofoutput from the first position detection circuit or the second positiondetection circuit, and cross-correlate a signal value string in theposition section and a third reference signal value string that is atleast a part of one of a plurality of the mode signal value strings eachof which is for identifying a different one of the signal modes; acumulative addition circuit operable to cumulatively add correlationvalues calculated by the third correlation circuit to the plurality ofmode signal value strings N times, N being a natural number; and a modespecification circuit operable to specify, from among the plurality ofmode signal value strings, a mode signal value string having a highestvalue cumulatively added by the cumulative addition circuit, as a signalmode of the input signal string.
 22. The signal detection circuit ofclaim 16, further comprising: a first-position detection circuitoperable to detect a first position in the correlation value stringoutput by the correlation circuit, the first position being based on aposition of a correlation value viewed as a maximum or a local maximum;and a second position detection circuit operable to detect a secondposition in the correlation value string compensated by the compensationcircuit, the second position being based on a position of a correlationvalue viewed as a maximum on the compensated correlation value string,wherein the mode detection circuit comprises: a third correlationcircuit operable to (i) output correlation values with respect to acertain mode signal value string by specifying a position section of amode signal value string in the input signal with use of output from thefirst position detection circuit or the second position detectioncircuit, and cross-correlating a signal value value string that is atleast a part of one of a plurality of the mode signal value strings eachof which is for identifying a different one of the signal modes, and(ii) output values obtained by inverting a sign of the correlationvalues as correlation values with respect to another mode signal valuestring; a cumulative addition circuit operable to cumulatively addcorrelation values calculated by the third correlation circuit to theplurality of mode signal value strings N times, N being a naturalnumber; and a mode specification circuit operable to specify, from amongthe plurality of mode signal value strings, a mode signal value stringhaving a highest value cumulatively added by the cumulative additioncircuit, as a signal mode of the input signal string.
 23. A signaldetection method for performing compensation by (i) obtaining acorrelation error of at least one correlation value on a correlationvalue string that is based on a result of cross-correlating a referencesignal value string included in a signal value string and signal valuestrings that are obtained by shifting a certain signal value string oneby one in order of the signal value string and that correspond in lengthto the reference signal value string, and (ii) suppressing thecorrelation error from the at least one correlation value.
 24. Acomputer for causing a signal detection device or a signal detectioncircuit to execute signal detection processing, wherein the signaldetection processing includes a compensation step of performingcompensation by (i) obtaining a correlation error of at least onecorrelation value on a correlation value string that is based on aresult of cross-correlating a reference signal value string included ina signal value string and signal value strings that are obtained byshifting a certain signal value string one by one in order of the signalvalue string and that correspond in length to the reference signal valuestring, and (ii) suppressing the correlation error from the at least onecorrelation value.